For example, there are electronic devices such as a television receiver using an organic electro-luminescence (EL) display or a liquid crystal display. In such an electronic device, luminescence elements arranged in a matrix to form an organic display or a liquid crystal display are driven by a plurality of thin film transistors (TFT).
TFT is formed, for example, by sequentially stacking, on a substrate, a source electrode and a drain electrode, a semiconductor layer (channel layer), and a gate electrode. The channel layer used in the TFT is generally a thin-film silicon semiconductor (for example, Patent Literature 1).
Silicon semiconductor films are classified into amorphous silicon films (amorphous silicon: a-Si) and silicon films having crystallinity (crystalline silicon films). Crystalline silicon films can be further classified into polycrystalline silicon films, microcrystalline silicon films, monocrystalline silicon films, and the like.
Among them, amorphous silicon films can be manufactured homogeneously on a large-area substrate at a relatively low temperature by chemical vapor deposition (CVD) method or the like. Nowadays, amorphous silicon films are most commonly used as channel layers for liquid crystal elements of a large screen. However, amorphous silicon films have properties such as carrier mobility which is deteriorated in comparison to crystalline silicon films. Therefore, in order to achieve displays with higher-speed driving and higher definition, it is desired to implement TFTs made of crystalline silicon films.
Meanwhile, examples of methods of forming a crystalline silicon film are a method of directly forming a crystalline silicon film in film forming (for example, Patent Literature 2) and a method of applying heat or light energy to a formed amorphous silicon film to be crystallized (for example, Patent Literature 3).
However, the crystalline silicon films formed by these methods have totally different film quality. In addition, even if crystalline silicon films are manufactured by the same method, they may have different film quality depending on crystallization conditions.
In general, regarding a semiconductor device having a crystalline semiconductor film as an active layer, it is known that film quality (such as crystallinity and defect density) of the active layer significantly affects properties of the device. In other words, in a transistor element having a crystalline silicon film as a channel layer, film quality of the crystalline silicon film significantly affects properties of the element, such as carrier mobility, a threshold voltage, and reliability.
For the above reasons, in order to use a crystalline semiconductor film as an active layer in a semiconductor device, it is necessary to evaluate and manage quality of the film. For the film quality management, it is desirable to manage, in particular, crystallinity.
As techniques of evaluating crystallinity of crystalline semiconductors, methods using Transmission Electron Microscope (TEM), X-ray Diffraction Technique (XRD), Photo Luminescence (PL), and the like are generally used. However, these techniques have difficulty in conducting in-line non-destructive evaluations of microscopic regions in a short period of time.
Therefore, there is Raman spectroscopy as a technique satisfying the above requirements (conducting the in-line non-destructive evaluations of microscopic regions in a short period of time).
The following describes the Raman spectroscopy with reference to the drawings.
FIG. 25 is a diagram schematically showing Raman scattering by incident light and molecular energy exchange.
Raman scattering is phenomenon caused by interaction between light and atoms oscillating in a material. More specifically, Raman scattering is phenomenon where, when light with oscillation frequency v0 is incident onto a material in which nucleus is oscillating with oscillation frequency v, two waves having the different oscillation frequencies intervene with each other and light with oscillation frequency v0+v and light with oscillation frequency v0−v are incident together with the light with oscillation frequency v0.
Here, as shown in (b) in FIG. 25, light scattering providing the same oscillation frequency as that of the incident light is called Rayleigh scattering, and light scattering providing oscillation frequency v0±v is called Raman scattering. Among the Raman scattering, components having oscillation frequency v0−v are called Stokes scattering ((a) in FIG. 25), and components having oscillation frequency v0+v are called Anti-Stokes scattering ((c) in FIG. 25) to be distinguished from each other.
Furthermore, an oscillation frequency difference ±v between incident light and Raman scattering light is called Raman shift. As this Raman shift is unique to a material, the Raman shift is a useful clue for material properties.
As explained above, the Raman spectroscopy is a technique of irradiating laser light to a specimen and measuring occurred Raman scattering light to easily perform non-destructive non-contact measurement and microscopic region evaluation. As a result, microscopic physicality can be examined.
For example, Patent Literature 4 discloses a method of manufacturing a semiconductor device by managing crystallinity of a crystalline silicon film by Raman spectroscopy. Patent Literature 4 discloses a method by which, when a-Si is laser-crystallized to be formed, the crystallization is performed observing a waveform or a full-width at half maximum (or FWHM) of a Raman peak as the crystallization state. In addition, for example, Patent Literature 5 discloses a method of managing crystallinity of a crystalline silicon film based on a Raman spectrum measured by Raman spectroscopy. It is disclosed in Patent Literature 5 that a crystalline silicon film is formed on a substrate, a peak waveform of a Raman band corresponding to a phonon unique to the crystalline silicon film is measured by Raman spectrometry, and crystallinity is managed based on a degree of asymmetry of this peak waveform.